The present invention relates to ultrasonic underwater detection apparatuses.
The invention will be explained as embodied in a fish finder installed in a ship, for detecting underwater conditions beneath the own ship.
FIG. 1 is a general block diagram of a conventional fish finder 51 comprising one transmit-receive channel. The fish finder is generally used in a bad environment having various background noises such as a ship""s running noise and noises produced in the ship. A trap circuit 1 supplies a 50 kHz transmitting burst signal S fed from a transmitter 2 to a transducer 3a and delivers a received echo signal fed from the transducer 3a to a preamplifier 4.
The transducer 3a is connected to the trap circuit 1 by means of two electric conductors. The length of the two electric conductors is, for example, more than five meters depending on the size of the own ship. The received echo signal from the transducer 3a mainly containing a 50 kHz component is mixed with a 300 kHz locally generated signal in a mixer 5. A frequency-converted output signal of the mixer 5 is entered to a filter 6, which passes only a 250 kHz analog received signal component whose frequency is equal to the difference between the frequencies of the raw received signal and the locally generated signal. The 250 kHz analog received signal is then amplified by a main amplifier 7 and converted into a digital signal by an analog-to-digital (A/D) converter 8. The digital received signal output from the A/D converter 8 is converted into a video signal suited for on-screen display by a display circuit 9 and this video signal is stored in a video random-access memory (RAM) provided in the display circuit 9. The video signal stored in the video RAM is converted back to an analog signal, which is delivered to a monitor 10, whereby underwater situations under the ship detected along a track of the ship on which the fish finder 51 is installed are displayed.
The trap circuit 1 is essentially a resonant circuit formed of a coil L and a capacitor C, and has a single resonant frequency. For this reason, the trap circuit 1 is designed to have a resonant frequency of 50 kHz when the operating frequency of the transducer 3a is 50 kHz. Accordingly, only one transducer 3a having the same resonant frequency as the trap circuit 1 can be connected to the trap circuit 1 and, therefore, it has been necessary to replace the fish finder when the transducer 3a has been replaced with one having an operating frequency of 200 kHz, for example.
There have been used various frequencies such as 15 kHz, 28 kHz, 38 kHz, 50 kHz, 88 kHz, 150 kHz or 200 kHz to excite ultrasonic transducers for fish finders. Various fish finders corresponding to these kinds of transducers respectively have to be manufactured and provided to users.
When a transducer which had been installed in the ship is desired to be used, there could be used only one type of fish finder operating on the same frequency as the operating frequency of the transducer.
Sounding the same area with two different frequencies produces such an advantageous effect that a comparison of echoes taken with the two frequencies allow easy discrimination of fish species in fish schools X or of the nature of a sea floor. To enable dual-frequency sounding, a conventional dual-frequency fish finder has two channels of transmitting and receiving circuits, two transducers 3a of different frequencies connected to the respective channels, and a monitor 10 which presents echoes of the two frequencies side by side on a single screen divided into two display areas as shown in FIG. 2.
Provision of the two-channel transmitting and receiving circuits, however, results in an increase in the mechanical size of the fish finder as well as in equipment cost.
The present invention has been made to solve the aforementioned problems of the prior art.
An object of the present invention is to provide an ultrasonic underwater detection apparatus which is capable of operating on a wide range of transducer frequencies and performing multi-frequency transmission and reception with a one-channel circuit configuration.
Another object of the invention is to provide an underwater detection apparatus which is capable of meeting demands from users in terms of frequency desired by the users.
Another object of the invention is to provide an underwater detection apparatus which simplifies manufacture and inventory control of fish finders, and the like.
Another object of the invention is to provide an underwater detection apparatus which can be connected to an ultrasonic transducer unit which is capable of transmitting or receiving signals having any one of carrier frequencies used in the fishing industry.
Another object of the invention is to provide an underwater detection apparatus which is capable of selecting and using an ultrasonic transducer unit having an operating frequency from a plurality of ultrasonic transducer units having mutually different operating frequencies.
Another object of the invention is to provide an underwater detection apparatus which is capable of selecting an operating frequency, or a combination of multiple operating frequencies, from a wide range of transducer frequencies and performing either single-frequency or multi-frequency transmission and reception with a one-channel circuit configuration, thereby eliminating the need to replace the fish finder when using a transducer having a different operating frequency.
According to an aspect of the invention, an underwater detection apparatus comprises a transducer for transmitting and receiving ultrasonic signals into and from the water, a transmitter for generating a transmission signal, a broadband trap circuit connected to the transducer by two conductive lines of a length more than five meters for transferring the transmission signal from the transmitter to the transducer and for passing an echo signal from the transducer, a preamplifier for amplifying the echo signal from the trap circuit, a mixer for converting the echo signal from the preamplifier into a signal of a specific frequency, a filter for selectively passing the signal of the specific frequency-band output from the mixer, a main amplifier for amplifying the echo signal from the filter, an A/D converter for converting the echo signal from the amplifier into a digital form, and an indicator for displaying the echo signal from the A/D converter.
Since the trap circuit does not include a resonant circuit, it has a broadband applicability, working independently of the frequency. Thus, operation of the trap circuit is not limited to any single transmitting frequency of the transmitter. Rather, the transmitting frequency of the transmitter may be determined according to the operating frequency of the transducer. If the transmitting frequency of the transmitter is freely variable, it would be possible to use a transducer having a desired operating frequency.
According to another aspect of the invention, an underwater detection apparatus comprises a first transducer for transmitting and receiving ultrasonic waves on its operating frequency F1, a second transducer for transmitting and receiving ultrasonic waves on its operating frequency F2, a transmitter for generating a transmitting signal, a trap circuit for transferring the transmitting signal fed from the transmitter to the transducers and for passing an echo signal fed from the transducers, a preamplifier for amplifying the echo signal fed from the trap circuit, a mixer for converting the echo signal fed from the preamplifier into a signal of a specific frequency, a filter for selectively passing the signal of only the specific frequency output from the mixer, a main amplifier for amplifying the echo signal fed from the filter, an A/D converter for converting the echo signal fed from the main amplifier into a digital form, and a display circuit for displaying the digitized echo signal fed from the A/D converter on a monitor, wherein the trap circuit includes a coil and a diode, or a resistor and a diode, the first transducer and the second transducer are connected in parallel to the trap circuit via a low-pass filter and a high-pass filter, respectively, the transmitting signal of the transmitter is alternately switched between the operating frequency F1 of the first transducer and the operating frequency F2 of the second transducer, and wherein a locally generated signal fed into the mixer is alternately switched between two specific frequencies such that the mixer constantly outputs the signal of the fixed frequency regardless of whether the input echo signal has the operating frequency F1 or F2.
Since the trap circuit has a broadband applicability, it is possible to use the first and second transducers having two different operating frequencies F1, F2, for example. With the low-pass filter and the high-pass filter connected to the first and second transducers, respectively, the transmitter can alternately outputs signals of the two frequencies F1, F2. Further, the locally generated signal supplied to the mixer is alternately switched between the two specific frequencies so that the mixer always outputs the signal of the fixed frequency regardless of the operating frequencies F1, F2.
According to another aspect of the invention, the first transducer has a low impedance at the operating frequency F1 and a high impedance at the operating frequency F2 while the second transducer has a low impedance at the operating frequency F2 and a high impedance at the operating frequency F1. This arrangement makes it possible to connect the two transducers in parallel with each other without using the low-pass filter and the high-pass filter.
According to another aspect of the invention, a transducer having two resonance points and usable at two operating frequencies F1, F2 is connected to the trap circuit instead of the first and second transducers.
It will be understood from the present Specification that since the underwater detection apparatus of the invention employs a broadband trap circuit and a low-gain preamplifier having good linearity to eliminate, where necessary, harmonic noise, it is possible to connect transducers of various operating frequencies. Furthermore, as the invention makes it possible to transmit and receive signals of multiple frequencies with a one-channel circuit configuration using transducers having different operating frequencies, it is possible to provide a highly-functional small-sized fish finder at low cost.
According to further aspect of the invention, an underwater detection apparatus comprises at least one transducer for transmitting and receiving ultrasonic signals, a transmitting signal generator for generating a transmitting signal of at least one frequency for driving the at least one transducer, a broadband trap circuit comprising a coil and a diode, or a resistor and a diode for transferring the transmitting signal fed from the transmitting signal generator to the at least one transducer selectively installed from multiple transducers and for passing an echo signal fed from the at least one transducer, a preamplifier for amplifying the echo signal fed from the trap circuit, a mixer for converting the echo signal of the at least one frequency fed from the preamplifier into a signal of a specific frequency, and a filter for selectively passing the signal of only the specific frequency-band output from the mixer.
Yet, according to another aspect of the invention, an underwater detection apparatus comprises an ultrasonic transducer for transmitting and receiving ultrasonic signals, a transmitting signal generator for generating a transmitting signal of a frequency for driving said ultrasonic transducer, a broadband trap circuit for transferring the transmitting signal from the transmitting signal generator to said transducer and for passing an echo signal fed from said ultrasonic transducer, a mixer for converting the echo signal of the frequency from said ultrasonic transducer into a signal of a specific frequency, a narrowband filter for selectively passing the signal of only the specific frequencies from said mixer, an amplifier for amplifying the echo signal from the filter, an A/D converter for converting the echo signal from the amplifier into a digital form, and an indicator for displaying the echo signal from the A/D converter.
According to another aspect of the invention, an underwater detection apparatus comprises an ultrasonic transducer for transmitting and receiving ultrasonic signals of a frequency, a transmitting signal generator capable of generating transmitting signals of a plurality of frequencies and outputting a signal of a frequency selected for driving said ultrasonic transducer, a broadband trap circuit for transferring the transmitting signal from the transmitting signal generator to said transducer and for passing an echo signal fed from said ultrasonic transducer, a local oscillator capable of generating local signals of a plurality of frequencies, a mixer for converting the echo signal of the frequency from said ultrasonic transducer into a signal of a specific frequency based on the echo signal and the local signal of a corresponding frequency selected, a narrowband filter for selectively passing the signal of only the specific frequencies from said mixer, an amplifier for amplifying the echo signal from the filter, an A/D converter for converting the echo signal from the amplifier into a digital form, and an indicator for displaying the echo signal from the A/D converter.
According to another aspect of the invention, an underwater detection apparatus comprises a first transducer for transmitting and receiving ultrasonic signals on its operating frequency F1, a second transducer for transmitting and receiving ultrasonic signals on its operating frequency F2, a transmitter for generating transmitting signals of the two frequencies at different times, a broadband trap circuit for transferring the transmitting signal from the transmitter to the transducers and for passing an echo signal from the transducers, a preamplifier for amplifying the echo signal from the trap circuit, a mixer for converting the echo signal from the preamplifier into a signal of a specific frequency, a filter for selectively passing the signal of only the specific frequency output from the mixer, a main amplifier for amplifying the echo signal from the filter, an A/D converter for converting the echo signal from the main amplifier into a digital form, and a display circuit for displaying the digitized echo signal from the A/D converter on a monitor.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings.